Whether the paroxysmal discharge be primary, or secondarily generalized from a focus in the cortex, consciousness is lost if the seizure discharge involves much of the brain.

Cerebral nerve cells are connected to other nerve cells in the spinal cord. The powerful generalized cortical seizure discharge is therefore linked through this direct transmission system to muscle fibres. Disordered contraction of all muscles is the hallmark of a grand mal seizure.

The first phase of a grand mal seizure is known as the tonic (contraction) phase. At this stage, because of widespread contraction of muscles, the body is rigid, and is incapable of maintaining a normal coordinated posture, so that the person falls to the ground. The respiratory muscles also contract, forcing out the air in the chest, so there may be an involuntary noise—a grunt or a cry—at the onset of the attack. The jaw muscles also contract, and, because the normal associated movements that keep the tongue out of the way are disordered by the seizure discharge, the tongue or inside of the cheek may be bitten.

During the tonic phase there are no coordinated movements of breathing, yet muscular contraction caused by the seizure discharge is vigorous. This combination means that the oxygen in the blood is rapidly used up, and the subject will become a dusky blue colour, the technical name for which is cyanosis. This colour is exaggerated by dilatation of blood vessels in the face by raised pressure within the thorax, due to the strong contraction of chest muscles. Normal movements of swallowing are lost, so that saliva may dribble out between the tightly clenched teeth. The disordered contraction of abdominal and bladder muscles may result in incontinence of urine, though this is by no means invariable. Dilatation of the pupils and sweating often occur.

After one or two minutes of the tonic phase, the seizure passes into the clonic or convulsive phase, with rhythmic movements of limbs and trunk muscles. These gradually cease after a few minutes, and the child or adult lies passively unconscious, often breathing stertorously. Normal colour returns. Consciousness gradually lightens, so that they can be roused, then begin to move around, and then can be helped to their feet and a chair. For several minutes after this, they will be confused and restless. After this they may suffer a headache for the rest of the day, or go to bed and sleep for a couple of hours. They will also be aware of stiff and painful muscles which have contracted forcibly during the seizure.

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